Chemical and mineralogical factors affecting the kinetics of acid drainage in different geomaterials

Abstract

Context

Acid drainage (AD) production from sulfide rich materials can impact the environment, particularly the surrounding mine areas. A suitable evaluation of AD is warranted to prevent and remediate its impacts. The methods that estimate AD and its kinetics are time consuming.

Aims

To identify chemical and mineralogical features that influence the AD dynamics, and propose a fast method to estimate the AD generation.

Methods

Chemical analyses of sulfides rocks and thiomorphic soil samples included pH, contents of major elements and the acid-base accounting (ABA). Mineral identification was performed by X-ray diffractometry (XRD) and scanning electronic microscopy (SEM). The rate of sulfide oxidation in samples was evaluated through simulated weathering (SW) tests performed with different contents of H₂O₂, with and without CaCO₃. Supernatant was drained to determine pH, acidity and S-sulfate.

Key results

Generation of AD was affected by carbonates and sulfides contents in samples, crystal sizes and types. Coal and thiomorfic soil produces more AD, due to framboidal pyrites and small sized sulfides.

Conclusions

Sulfides oxidation rate and AD generation increased from the metamorphic and igneous intrusive rocks to sedimentary-volcanic and then the supergenic geomaterials, from bigger to smaller crystal sizes. Carbonates and arsenic inhibit AD kinetics. The ABA failed to predict the AD in geomaterials, especially the ultramafic. The SW dynamic tests were suitable to assess AD kinetics and the stoichiometry of acidity production.

Implications

Carbonates and sulfides are important features to predict AD in several geological environments. Using H₂O₂ can abreviate the time consuming tests to assess the AD kinetics.